Microelectromechanical system (MEMS) resonators are used for multiple applications, among them low-power, low-phase noise, high stability oscillators. Connecting the MEMS resonators to the circuit as well as packaging are usually challenging aspects of such designs. Multiple approaches have been used, such as: wire-bonding, flip-chip MEMS, CMOS-MEMS, etc. Each approach includes a set of challenges that may limit its application to niche areas.
A thin-film bulk acoustic wave (BAW) resonator is a MEMS device that includes a piezoelectric material sandwiched between two electrodes and acoustically isolated from the surrounding medium. MEMS resonator devices using piezoelectric films with thicknesses ranging from several micrometers down to tenth of micrometers resonate in the frequency range of roughly 100 MHz to 10 GHz. Aluminum nitride and zinc oxide are two common piezoelectric materials used in MEMS resonators.
Several types of MEMS resonator based oscillators are known, see for example: Padimarri, Arun, Nathan Ickes, and Anantha P. Chandrakasan, “A 0.68V 0.68 mVV 2.4 GHz PLL for Ultra-Low Power RF Systems.” 2015 IEEE Radio Frequency Integrated Circuits Symposium (RFIC) (May 2015); A. Nelson, J. Hu, J. Kaitila, R. Ruby and B. Otis, “A 22 μW, 2.0 GHz FBAR oscillator,” 2011 IEEE Radio Frequency Integrated Circuits Symposium, Baltimore, Md., 2011, pp. 1-4. A high-Q MEMS-based oscillators may have moderate power consumption, low phase noise, and high accuracy/stability.
Other solutions to generate low power clocks in the GHz range include ring oscillators and LC (inductor-capacitor) oscillators. Ring oscillators usually produce relatively high power consumption in the milli-watt range (mW's), produce very high phase noise, and may have poor stability. LC oscillators also produce high power consumption (mW's), while providing moderate phase noise and poor stability. In some designs, power consumption may be reduced by reducing supply voltage or adjusting biasing of transistors in the oscillator circuit.
Other features of the present embodiments will be apparent from the accompanying drawings and from the detailed description that follows.